n1 = 0.75
n2 = 0.675000
n3 = 0.607500
n4 = 0.546750
ans = n1 + 2*((1-n1)*n2) + 3*((1-n1)*(1-n2)*n3) + 4*((1-n1)*(1-n2)*(1-n3)*n4)
print(ans)